The present invention is directed to a process of preparing starch phosphate monoesters, optionally in the presence of oligosaccharides, having improved reaction efficiency and reduced side reactions. The invention also includes the improved starch phosphate monoester products, which are characterized by high viscosity and a low level of residual salt, their use in food and the enhanced food compositions prepared from them.
Starch phosphate monoesters are anionic derivatives that yield higher-viscosity, clearer, and more stable dispersions than unmodified starch. Solarek, D. B., Phosphorylated Starches and Miscellaneous Inorganic Esters: Properties and Uses, CRC Press, Boca Raton, 1986, page 103. Increasing the level of phosphate substitution on starch phosphate monoesters results in desirably lower gelatinization temperatures. Id. However, increased phosphorylation levels also often results in a product with higher levels of residual inorganic phosphate salt. It is known that the viscosity of the starch phosphate monoester products is sensitive to salt and pH conditions. Id.
Traditional methods of phosphorylating starch generally require the impregnation of the base starch with an alkali-metal phosphate followed by heating to effect the phosphorylation process. A common manufacturing procedure is exemplified by U.S. Pat. No. 4,166,173, which describes the treatment of a starch cake with a 2-30% by weight aqueous solution of an alkali metal tripolyphosphate salt. The treated starch cake is then dried to a moisture content of less than 20% and heated to effect phosphorylation. In general, moisture content prior to the heat treatment is limited broadly to less than 20% in order to keep water from interfering in the phosphorylation reaction. Heat treatment effecting the phosphorylation of the starch is most often carried out in convection or vacuum ovens and conventional dextrinizers.
Starch phosphate monoesters have also been produced via fluidized bed technology. U.S. Pat. No. 3,284,443, describes the phosphorylation of starch which is carried out in a fluidized bed reactor as a continuous and batch process at moisture contents of less than twenty percent, and high temperatures of between 149 to 232xc2x0 C. The high temperature of this process combined with long reaction periods results in high level of bound phosphorus and thus good reaction efficiency. However, it is known that high temperature and long reaction periods induce significant starch hydrolysis resulting in products with low viscosity and low purity that are unsuitable for use in food due to off-color and undesirable taste.
U.S. Pat. No. 3,843,377 and WO 99/64467 also suggest the use of a fluidized bed reactor in order to heat treat blends of starch and urea under semi-dry conditions of less than 5% moisture at temperatures of between 100 to 175xc2x0 C. for between 20 to 60 minutes. These processes result in a large amount of bound nitrogen as well as bound phosphorus on the starch. In addition, the process undesirably releases ammonia as a side product. As a result, these products are unsuitable for certain uses, such as food applications. The use of a fluidized state to achieve substantially anhydrous conditions, conditions in which the moisture content is kept to less than 1%, is unknown.
Known processes do not proceed with a high reaction efficiency at low temperatures and short reaction times, thus minimizing side reactions and residual inorganic salts. There remains a need for an efficient process which produces relatively pure and high viscosity starch phosphate monoesters with less residual inorganic phosphate salt. The improved products of such an efficient process should desirably demonstrate enhanced viscosity, color and good moisture retention properties which are useful in a variety of applications, particularly as food additives.
The use of starch phosphate monesters in food has been described for a variety of high moisture food systems such as gravies, salad dressings, puddings, sour cream, bakery creams and milk as well as intermediate and low moisture food products such as meat, imitation cheese, baked products and frozen foods. In most cases, starch phosphate monoesters are used as viscosifiers in order to provide texture and/or stability. Further, JP62248470, describes the use of a starch phosphate monoester to improve the elasticity, water retention and stickiness of meat pastes and fish products. In addition, U.S. Pat. Nos. 4,499,116, 4,608,265, 4,695,475 and 4,937,091 describe the use of pregelatinized, pregelatinized and converted as well as pregelatinized and enzyme treated phosphorylated starch monoesters in imitation cheese. However, these products have inferior gelling and cohesion properties, and thus do not have a desirably firm texture and tend to mat.
There remains a need to provide improved starch phosphate monoesters for use as additives to impart a variety of desirable textures, flavor, color and moisture retention properties, particularly in food products containing protein and having low to intermediate moisture content.
The present invention is directed to a process of preparing starch phosphate monoesters with improved reaction efficiency and reduced side reactions. The process may be conducted optionally in the presence of oligosaccharides. The invention also includes the starch phosphate monoester products which are characterized by improved viscosity, color and moisture retention properties. The invention further relates to the use of the starch phosphate monesters to improve the texture, color and moisture retention in food, particularly protein containing food having a low to intermediate moisture content, as well as the food compositions prepared therefrom.